ERRATA. 
P. 25, line 12, for ‘‘p. 29” read ‘‘ p. 27.” 
P. 53, line 23, for ‘‘p. 36” read ‘* p. 35.” 
P, 233, under illustration, for ‘‘ convolution ”’ read “‘ convolutions. 
P. 249, line 11, for ‘* 600 gallons’’ vead ‘‘ 4oo gallons.” 
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